1. Field of the Invention
The present invention relates to a fuel cell system. In particular, it relates to a fuel cell system mounted to an automobile.
2. Related Art
In recent years, a fuel cell system gains a spotlight as a new power source of an automotive vehicle. For example, a fuel cell system is provided with a fuel cell producing electric power from chemical reaction of reactive gas, a reactive gas supply device supplying reactive gas to the fuel cell through a reactive gas channel, and a control device controlling this reactive gas supply device.
For example, the fuel cell consists of a plurality, e.g., tens or hundreds, of stacked cells. Each of the cells is configured so that a pair of separators sandwiching a membrane electrode assembly (MEA) which consists of two electrodes, which are an anode (positive) electrode and a cathode (negative) electrode, and a solid polymer electrolyte membrane sandwiched by these electrodes.
Supplying hydrogen gas and oxygenated air to the anode electrode and the cathode electrode of the fuel cell, respectively, causes electrochemical reaction to generate electric power.
By the way, in the above-mentioned fuel cell system, hydrogen gas is supplied from the hydrogen tank to the fuel cell, and hydrogen off-gas is discharged from the fuel cell. Since the amount of hydrogen is contained in hydrogen gas supplied from the hydrogen tank is more than that of hydrogen necessary for power generation, excess hydrogen is contained in the exhausted hydrogen off-gas from the fuel cell. Then, hydrogen off-gas is collected by using a circulation unit to be supplied to the fuel cell, together with hydrogen gas from the hydrogen tank.
This circulation unit needs no external power source and uses an ejector utilizing pressure energy, in many cases. For example, the ejector is provided with a housing, a needle provided in this housing to be capable of moving forward and backward, and an approximately cylindrical nozzle provided in the housing to accommodate the needle (see Japanese Published Unexamined Patent Application Publication No. 2002-227799).
Hydrogen gas from the hydrogen tank is introduced into the nozzle, and hydrogen off-gas is introduced into the exhaust port of the nozzle. In addition, an air extreme pressure introducing chamber, into which signal pressure is introduced, is provided at the bottom end side of the needle. A fuel extreme pressure introducing chamber is provided adjacent to this air extreme pressure introducing chamber, and hydrogen off-gas as back pressure is introduced into this fuel extreme pressure introducing chamber through a pipe. A first diaphragm separates the air extreme pressure introducing chamber and the inside of the nozzle. A second diaphragm separates the air extreme pressure introducing chamber and the fuel extreme pressure introducing chamber.
According to this ejector, the needle moves forward and backward according to the differential pressure between the air extreme pressure introducing chamber and the fuel extreme pressure introducing chamber to adjust the flows of hydrogen off-gas to be collected and hydrogen gas to be supplied to fuel cell.
However, in the structure described in the above-mentioned patent application, pressure fluctuation is propagated to the air extreme pressure introducing chamber through the first diaphragm when the pressure of hydrogen gas introduced from the hydrogen tank fluctuates. Accordingly, there has been a problem that signal pressure to be introduced into the air introducing chamber also fluctuates, resulting in that the flow of hydrogen gas to be supplied from the ejector to the fuel cell fluctuates. Therefore, it is necessary to provide with a regulator controlling the pressure of hydrogen gas to be introduced into the ejector.
An object of the present invention is to provide an ejector capable of maintaining the constant flow of gas to be delivered even if the pressure of introduced gas fluctuates.